Device and method for providing wavelength reduction with a photomask

ABSTRACT

Disclosed is a photomask having a wavelength-reducing material that may be used during photolithographic processing. In one example, the photomask includes a transparent substrate, an absorption layer having at least one opening, and a layer of wavelength-reducing material (WRM) placed into the opening. The thickness of the WRM may range from approximately a thickness of the absorption layer to approximately ten times the wavelength of light used during the photolithographic processing. In another example, the photomask includes at least one antireflection coating (ARC) layer.

BACKGROUND

This application claims benefit and priority from U.S. ProvisionalPatent Application Ser. No. 60/511,503, filed on Oct. 15, 2003 andentitled “Device and Method for Providing Wavelength Reduction with aPhotomask”.

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing have been needed.

For example, in the course of integrated circuit evolution, functionaldensity (i.e., the number of interconnected devices per chip area) hasgenerally increased while feature size (i.e., the smallest component orline that can be created using a fabrication process) has decreased.This scaling down process generally provides benefits by increasingproduction efficiency and lowering associated costs, but needs to bematched by improvements in the fabrication process. For instance, manyfabrication processes utilize a photomask to form a pattern duringphotolithography. The pattern may contain a pattern of designed circuitsthat will be transferred onto a semiconductor wafer. However, because ofthe increasingly small patterns that are to be used duringphotolithography, photomasks have generally needed increasingly highresolutions.

SUMMARY

In one embodiment, the present disclosure provides a photomask forforming a pattern during photolithography when illuminated with apredetermined wavelength of light. The photomask comprises a transparentsubstrate; an absorption layer proximate to the substrate, wherein theabsorption layer has at least one opening formed therein; and a layer ofwavelength-reducing material disposed in at least one opening, wherein athickness of the wavelength-reducing material and the absorption layerform a generally planar surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of one embodiment of aphotomask with a wavelength reducing medium.

FIG. 2 is a flow chart of an exemplary method for forming the photomaskof FIG. 1.

FIGS. 3 a-3 c illustrate various fabrication stages of the photomask ofFIG. 1 as it is formed using the method of FIG. 2.

FIG. 4 illustrates a cross-sectional view of another embodiment of aphotomask with a wavelength reducing medium.

FIG. 5 is a flow chart of an exemplary method for forming the photomaskof FIG. 4.

FIGS. 6 a-6 c illustrate various fabrication stages of the photomask ofFIG. 4 as it is formed using the method of FIG. 5.

FIG. 7 illustrates a cross-sectional view of yet another embodiment of aphotomask with a wavelength reducing medium.

FIG. 8 is a flow chart of an exemplary method for forming the photomaskof FIG. 7.

FIGS. 9 a-9 c illustrate various fabrication stages of the photomask ofFIG. 7 as it is formed using the method of FIG. 8.

DETAILED DESCRIPTION

The present disclosure relates generally to photolithography and, moreparticularly, to using a wave-length reducing medium with a photomask.It is understood, however, that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Referring to FIG. 1, a cross-sectional view of one embodiment of aphotomask 100 is illustrated. The photomask 100 comprises a transparentsubstrate 102, an absorption layer 104, and a wavelength-reducingmaterial (WRM) 106. The transparent substrate 102 may use fused silica(SiO2) or a glass relatively free of defects, such as borosilicate glassand soda-lime glass. Other suitable materials may also be used.

The absorption layer 104 may be formed using a number of differentprocesses and materials, such as depositing of a metal film made withChromium (Cr) oxide and iron oxide, or an inorganic film made with MoSi,ZrSiO, and SiN. The absorption layer 104 may be patterned to have one ormore openings 108 through which light may travel without being absorbedby the absorption layer. In some embodiments, the absorption layer 104may have a multi-layer structure, which may further include anantireflection (ARC) layer and/or other layers. In addition, some ofthese layers may be formed multiple times to achieve a desiredcomposition of the absorption layer 104.

The absorption layer 104 may be tuned to achieve a predeterminedtransmittance and an amount of phase shifting, enabling the absorptionlayer 104 to shift the phase of light passing through the absorptionlayer, for improved imaging resolution. For example, the transmittanceof the absorption layer 104 may be tuned to between approximately threepercent and thirty percent, while the phase shift is tuned toapproximately 180 degrees. This type of photomask is sometimes referredto as an attenuated phase-shifting photomask. In another example, thetransmittance of the absorption layer 104 may be extremely high (e.g.,95%), and the phase shift may be approximately 180 degrees. This type ofphotomask is sometimes referred to as a chromeless phase-shiftingphotomask.

The WRM 106 may be used to fill in the one or more openings 108 of theabsorption layer 104. The surface of the WRM 106 may be substantiallyco-planar with the surface of the absorption layer 104, but may be finetuned to be slightly higher or lower with the plane of the surface ofthe absorption layer 104. Both materials may be planarized using knownplanarization techniques, such as chemical-mechanical planarization(CMP) to form a planar surface. The thickness of the WRM 106 may varyfrom less than to about the thickness of the absorption layer 104 (e.g.,if the surface of the WRM is aligned with the surface of the absorber),to up to about ten times the wavelength of light passing through the WRM106 during photolithographic processing. The WRM material used for theWRM 106 may be chosen based on a desired level of transparency and adesired refractive index. The WRM 106 preferably has a refractive indexdifferent from that of the absorption layer. In the present example, theWRM material is selected to provide both a high level of transparencyand a high refractive index. Exemplary WRM materials include photoresistmaterials, polymer materials, and dielectric materials. For example, thematerial may include polyimide, SiO2, indium tin oxide (ITO), polyvinylalcohol (PVA), or silicone.

During a photolithography process, the photomask 100 is disposed above asemiconductor formation. Typically, the photomask 100 does not come intocontact with the surface of the semiconductor formation. Due to therelatively high refractive index (“n”) of the WRM 106, the wavelength ofthe light passing through the WRM 106 during photolithography processingmay be reduced by a factor of n from the wavelength of the light in avacuum. Since the physical size of the opening 108 in the absorptionlayer 104 remains the same, but the size of the opening 108 relative tothe wavelength of the light is enlarged by the factor of n, opticaldiffraction is reduced accordingly and the resolution of imaging of thephotomask 100 on a wafer may be enhanced.

Referring now to FIG. 2 and with additional reference to FIGS. 3 a-3 c,an exemplary method 150 may be used to form the photomask 100 of FIG. 1.The method 150 begins in step 152 with the formation of the absorptionlayer 104 above the transparent substrate 102 as shown in FIG. 3 a. Itis understood that the transparent substrate 102 may be cleaned orotherwise prepared using processes not illustrated in the presentexample of method 100. The absorption layer 104 may be formed using aprocess such as a physical vapor deposition (PVD) process, includingevaporation and sputtering, a plating process, including electrolessplating or electroplating, or a chemical vapor deposition (CVD) process,including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD),plasma enhanced CVD (PECVD), or high density plasma CVD (HDP CVD). Inthe present example, a sputtering deposition may be used to provide theabsorption layer 104 with thickness uniformity, relatively few defects,and a desired level of adhesion. As previously described with respect toFIG. 1, the absorption layer 104 may include materials such as Chromiumoxide, iron oxide, MoSi, ZrSiO, and SiN.

In step 154 (FIG. 3 b), the absorption layer 104 may be patterned tohave a predefined arrangement of openings 108 using known processes suchas a photolithography process or an electron beam process. For example,the photolithography process may include the following processing steps.A photoresist layer (not shown) may undergo a process involving spin-oncoating, baking, exposure to illuminated light through a photomask,developing, and post baking. This transfers the pattern from thephotomask to the photoresist. Next, a wet etching or dry etching may beused to etch an exposed region of the absorption layer 104 to transferthe pattern from the photoresist to the absorption layer. Thephotoresist may then be stripped by wet stripping or plasma ashing. Inthe present example, the patterned absorption layer has at least oneopening, as shown in FIG. 3 b.

In step 156 and with additional reference to FIG. 3 c, the WRM 106 maybe formed in the opening of the absorption layer 104 using a processsuch as a spin-on coating, CVD, atomic layer deposition, or PVD.Depending on a desired thickness of the WRM or upon a desired height ofthe WRM relative to the surface of the absorption layer 104, the surfaceof the WRM is substantially co-planar with the absorption layer, but maybe fine-tuned to be slightly higher or lower than the surface of theabsorption layer 104. A planarizing process, such as CMP may be used toplanarize the WRM 106 and the absorption layer 104. In the presentexample, the thickness of the WRM ranges from about the thickness of theabsorption layer 104 to approximately ten times the wavelength of lightpassing through the WRM during photolithography processing. The WRM mayuse a material of high transparency and high refractive index, includingphotoresist materials, polymer materials, and dielectric materials.Examples of WRM materials include polyimide, SiO2, ITO, PVA, andsilicone.

Referring now to FIG. 4, a cross-sectional view of another embodiment ofa photomask 200 is illustrated. The photomask 200 comprises atransparent substrate 202, an absorption layer 204, a WRM 206, and aplurality of antireflection coating (ARC) layers. As the transparentsubstrate 202, absorption layer 204, and WRM 206 are similar to thosedescribed with respect to FIG. 1, they will not be described in detailin the present example.

For purposes of illustration, the ARC layers may include an ARC layer210 on an underside (relative to the absorption layer 204) of thesubstrate 202, an ARC layer 212 between the substrate 202 and theabsorption layer 204, an ARC layer 214 between the absorption layer 204and the WRM 206, and/or an ARC layer 216 above the WRM 206. It isunderstood that the ARC layer 214 may not cover the sidewall of thepatterned absorption layer 204, depending on a particular processingsequence or processing method used to form the photomask 100.

The ARC layers 210, 212, 214, 216 may be used at an interface to reducestray light introduced by the photomask. Such interfaces may include aninterface between the substrate 202 and the absorption layer 204 (usingthe ARC layer 212), an interface between the absorption layer 204 andthe WRM 206 (using the ARC layer 214), and an interface between thesubstrate 202 and the WRM 206 (using the ARC layer 212), even thoughthese ARC layers may function differently. For example, the ARC layer214 on the absorption layer 204 may eliminate stray light contributed bythe high reflectivity of the absorption layer. The ARC layer 216 on theWRM 206 may reduce multiple reflections between the outer face of theWRM 206 and the absorption layer 204. It may also reduce the reflectionbetween the WRM 206 and the space outside. The ARC layer 212 on thesubstrate may reduce flare back into an illumination system used duringphotolithography and may provide a smooth transition between thesubstrate 202 and the WRM 206 to eliminate mismatch of the refractiveindex.

Each ARC layer may have multi-level structure that provides each ARClayer with multiple layers having different refractive indices. Forexample, the ARC layers may have a graded structure where the refractiveindex of each ARC layer changes gradually to match the refractiveindexes of neighboring materials in the photomask 100. The ARC layersmay comprise an organic material containing hydrogen, carbon, or oxygen;compound materials such as Cr2O3, ITO, SiO2, SiN, TaO5, Al2O3, TiN, andZrO; metal materials such as Al, Ag, Au, and In; or combination thereof.

Referring now to FIG. 5 and with additional reference to FIGS. 6 a-6 c,an exemplary method 250 may be used to form the photomask 200 of FIG. 4.The method 250 begins in step 252 with the formation of the ARC layer210 on the substrate 202, the formation of the ARC layer 212 on theother side of the substrate 202, the formation of the absorption layer204, and the formation of the ARC layer 214 above the absorption layer204.

As previously described, materials used for the absorption layer 204 mayinclude metal film such as Chromium (Cr) oxide and iron oxide, orinorganic films such as MoSi, ZrSiO, and SiN. The absorption layer 204may be formed using CVD, plating, or PVD processes. In the presentexample, sputtering deposition may be preferred to provide theabsorption layer 204 with thickness uniformity, relatively few defects,and better adhesion.

The ARC layers may use an organic material containing hydrogen, carbon,or oxygen; compound materials including Cr2O3, ITO, SiO2, SiN, TaO5,Al2O3, TiN, and ZrO; metal materials such as Al, Ag, Au, and In; orcombination thereof. Methods used to form the ARC layers include spin-oncoating, CVD, plating, or PVD.

In step 254, the absorption layer 204 and the ARC layer 214 may bepatterned to have a predefined arrangement of openings as previouslydescribed with respect to the method 150 of FIG. 2. The ARC layer 214may be patterned using a processing sequence similar to that used forthe absorption layer 204, but may use a different etchant. It is notedthat the ARC layer 214 does not cover the sidewalls of the absorptionlayer 204 (e.g., the walls of the openings 208). In step 256, the WRM206 may be formed and, in step 258, the ARC layer 216 may be formedusing similar materials and processing methods as those used in step252.

Referring now to FIG. 7, a cross-sectional view of yet anotherembodiment of a photomask 300 is illustrated. The photomask 300comprises a transparent substrate 302, an absorption layer 304, a WRM306, and a plurality of antireflection coating (ARC) layers. As thetransparent substrate 302, absorption layer 304, and WRM 306 are similarto those described previously, they will not be described in detail inthe present example.

For purposes of illustration, the ARC layers may include an ARC layer310 on an underside (relative to the absorption layer 304) of thesubstrate 302, an ARC layer 312 between the substrate 302 and theabsorption layer 304, an ARC layer 314 between the absorption layer 304and the WRM 306, and/or an ARC layer 316 above the WRM 306. These ARClayers are similar to those described with respect to FIG. 4, exceptthat the ARC layer 214 covers the sidewalls of the absorption layer 304(e.g., the walls of the openings 308).

Referring now to FIG. 8 and with additional reference to FIGS. 9 a-9 c,an exemplary method 350 may be used to form the photomask 300 of FIG. 7.The method 350 begins in step 352 with the formation of the ARC layer310 on the substrate 302, the formation of the ARC layer 312 on theother side of the substrate 302, and the formation of the absorptionlayer 304. Unlike the method 250 previously described, the ARC layer 314is not formed during this step.

In step 354, the absorption layer 304 may be patterned to have apredefined arrangement of openings as previously described and, in step356, the ARC layer 314 is formed. Since the ARC layer 314 is formedafter the absorption layer 304 is formed and patterned, the ARC layer314 conforms to the shape of the absorption layer 304. This enables theARC layer 314 to be formed over the sidewalls of the absorption layer304 (FIG. 8b). In step 358, the WRM 306 may be formed and, in step 360,the ARC layer 316 may be formed using similar materials and processingmethods as those used in step 352.

The present disclosure has been described relative to a preferredembodiment. Improvements or modifications that become apparent topersons of ordinary skill in the art only after reading this disclosureare deemed within the spirit and scope of the application. It isunderstood that several modifications, changes and substitutions areintended in the foregoing disclosure and in some instances some featuresof the invention will be employed without a corresponding use of otherfeatures. For example, one or more of the illustrated ARC layers may beexcluded or additional ARC layers may be used. Materials used for thetransparent substrate, absorption layer, wavelength reducing material,and ARC layers may vary, as may the method by which the various layersare formed. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theinvention.

1. A photomask for forming a pattern during photolithography whenilluminated with a predetermined wavelength of light, the photomaskcomprising: a transparent substrate; an absorption layer proximate tothe substrate, wherein the absorption layer has at least one openingformed therein; and a layer of wavelength-reducing material disposed inthe at least one opening, wherein the wavelength-reducing material andthe absorption layer form a generally planar surface.
 2. The photomaskof claim 1 wherein a thickness of the wavelength-reducing material issubstantially equal to a thickness of the absorption layer.
 3. Thephotomask of claim 1 wherein the wavelength-reducing material forms agenerally planar surface beyond the absorption layer.
 4. The photomaskof claim 1 wherein the wavelength-reducing material thickness is lessthan or equal to about ten times the predetermined wavelength of thelight.
 5. The photomask of claim 1 wherein the wavelength-reducingmaterial has a refractive index larger than 1 and a transmissivity ofmore than 10%.
 6. The photomask of claim 1 wherein thewavelength-reducing material comprises a transparent polymer material.7. The photomask of claim 1 wherein the wavelength-reducing materialcomprises a photoresist material.
 8. The photomask of claim 1 whereinthe wavelength-reducing material comprises a transparent dielectricmaterial.
 9. The photomask of claim 1 wherein the absorption layer has atransmissivity of between 1% and 100% and is adapted to modify a phaseof light passing through the absorption layer, and wherein thewavelength-reducing material has a refractive index larger than 1 and atransmissivity of more than 10%.
 10. The photomask of claim 1 whereinwavelength-reducing material has a refractive index different from thatof the absorption layer.
 11. The photomask of claim 1 further comprisingat least one antireflection coating layer.
 12. The photomask of claim 1further comprising at least one antireflection coating layer on thewavelength-reducing material.
 13. The photomask of claim 1 furthercomprising at least one antireflection coating layer on the substrate.14. The photomask of claim 1 further comprising at least oneantireflection coating layer between the absorption layer and thewavelength-reducing material.
 15. The photomask of claim 11 furthercomprising at least one antireflection coating layer between thewavelength-reducing material and the substrate.
 16. The photomask ofclaim 1 further comprising at least one antireflection coating layerbetween the absorption layer and the substrate.
 17. The photomask ofclaim 1 further comprising at least one antireflection coating layerwith a graded structure.
 18. A method for fabricating a photomask on atransparent substrate, the method compromising: forming an absorptionlayer proximate to the substrate; patterning the absorption layer andforming at least one opening in the absorption layer; and forming awavelength-reducing material in the at least one opening of theabsorption layer.
 19. The method of claim 18 further comprising formingan antireflection coating layer on a side of the substrate opposite thewavelength-reducing material.
 20. The method of claim 18 furthercomprising forming an antireflection coating layer on thewavelength-reducing material.
 21. The method of claim 18 furthercomprising forming an antireflection coating layer between the substrateand the wavelength-reducing material.
 22. The method of claim 18 furthercomprising forming an antireflection coating layer between the substrateand the absorption layer.
 23. The method of claim 18 further comprisingforming an antireflection coating layer between the wavelength-reducingmaterial and the absorption layer.
 24. The method of claim 18 whereinforming the wavelength-reducing material comprises a spin coatingprocess.
 25. The method of claim 18 wherein forming thewavelength-reducing material comprises a sputtering deposition process.26. The method of claim 18 wherein forming the wavelength-reducingmaterial comprises a chemical vapor deposition process.
 27. The methodof claim 18 wherein forming the wavelength-reducing material comprisesan atomic layer deposition process.
 28. The method of claim 18 whereinforming the wavelength-reducing material comprises a physical vapordeposition process.
 29. The method of claim 18 wherein forming thewavelength-reducing material comprises limiting a thickness of thewavelength-reducing material between about a thickness of the absorptionlayer to approximately ten times a predefined wavelength of light. 30.The method of claim 18 wherein forming the wavelength-reducing materialcomprises a planarizing process.
 31. A photomask comprising: asubstantially transparent substrate; an absorption layer proximate tothe substantially transparent substrate and defining at least oneopening therein; and a high refractive index layer disposed in the atleast one opening of the absorption layer and operable to reduce awavelength of light passing therethrough during photolithography.
 32. Aphotolithography method comprising: positioning a photomask above asemiconductor formation, the photomask comprising: a substantiallytransparent substrate; an absorption layer proximate to thesubstantially transparent substrate and defining at least one openingtherein; and a high refractive index layer disposed in the at least oneopening of the absorption layer and operable to reduce a wavelength oflight passing therethrough during photolithography; exposing thesemiconductor formation and photomask to light.